Файл: Microcontroller Programming. Thi Micro Chip PIC (Julio Sanchez, 2007).pdf

;=========================================================

; program

;=========================================================

main:

; Port-A is all output Bank1

movlw b’00000000’ movwf TRISA

;Port-B line 0 is input, all others are output movlw b’00000001’

movwf TRISB Bank0

;Make sure Port-A line 2 (clear line) is high movlw b’00000100’

movwf PORTA

;dataReg contains input ;===========================

;call serial output

;procedure ;===========================

call out164 ; Call serial output procedure

;===========================

;wait forever ;=========================== endloop:

goto endloop ;============================================================

;74HC164 procedure to send serial data ;============================================================

;ON ENTRY:

;local variable dataReg holds 8-bit value to be

;transmitted through port labeled serialLN

;OPERATION:

;1. A local counter (bitCount) is initialized to

;8 bits

;2. Code assumes that the first bit is zero by

;setting the data line low. Then the high-order

;bit in the data register (dataReg) is tested.

;If set, the data line is changed to high.

;3. Bits are shifted in by pulsing the 74HC164

;clock line (CLK).

;4. Data bits are then shifted left and the bit

;counter is tested. If all 8 bits have been sent

;the procedure returns.

;Using this assumption is possible because the bit is not

;shifted in until the clock line is pulsed.

;=========================

;pulse clock line ;=========================

;Bits are shifted in by pulsing the 74HC164 CLK line

;============================================================

;74HC165 procedure to read parallel data and send

;============================================================

;OPERATION:

;1. Eight DIP switches are connected to the input

;ports of an 74HC165 IC. Its output line Hout,

;and its control lines CLK and load are connected

;to the PIC’s Port-B lines 0, 1, and 2

;respectively

;2. Procedure sets a counter (bitCount) for 8

;iterations and clears a data holding register

;(dataReg).

;3. Port-B bits are read into w. Only the lsb of

;Port-B is relevant. Value is stored in a working

;register and the meaningful bit is rotated into

;the carry flag, then the carry flag bit is

;then shifted into the data register.

;4. The iteration counter is decremented. If this

;is the last iteration the routine ends. Otherwise

;the bitwise read-and-write operation is repeated.

;======================================================== end

14.5.4 TTYUsart Program

;File name: TTYUsart.asm

;Last update: May, 2006

; Author: Julio Sanchez

;Processor: 16F84A

;Description:

;Program to emulate USART operation in PIC code. Uses

;PIC-to-LCD interface. Display has 2 lines, each with

;16 characters.

;Program operation:

;Characters received from the RS232 line are displayed on

;the LCD. LCD lines scroll automatically. A pushbutton

;activates the send operation by transmitting the text

;string: Readywhich is also displayed on the LCD.

;

;Program communications and LCD parameters are stored in

;#define statements. These statements can be edited to

;accommodate a different set-up. Program uses delay loops

;for interface timing.

;

;WARNING:

;Code assumes 4Mhz clock. Delay routines must be

;edited for faster clock

;

;BAUD RATE CALCULATIONS:

;A 4Mhz clock oscillator has a clock frequency of 1 Mhz:

;Since the baud rate is the number of clock cycles per

;second, for a 4Mhz clock it is:

;bit time = ——— sec. = 208.33 microseconds

;4,800

;Calculating one half the baud rate allows resetting the

;clock from the edge to the center of a time pulse:

;

;|<======== falling edge of start bit

;| |

;208/2 = 104

;The PIC clock counts up from 0 to 255. So to implement

;a 104 microsecond delay we must start counting at

;clock beat:

;plus one microsecond for movlw instruction used to

;initialize the clock:

; For one full baud rate delay: